The present invention relates to the aircraft autopilot art and, in particular, to an improved autopilot system which allows the flight crew to maintain autopilot engagement while making a late runway change during approach.
A problem frequently encountered by commercial aircraft flight crews on approach to an airport is runway re-assignment. As the aircraft approaches an airport, it is assigned a runway and an approach profile by air traffic control. Due to various conditions that can occur, an aircraft is often re-assigned from one runway to another and is expected to make a smooth transition thereto. Such re-assignment may happen after the flight crew has engaged the autopilot and after the aircraft's on board instrument landing system (ILS) has captured either the assigned runway's localizer signal (which defines lateral movement within the approach profile) and/or glideslope (which defines the desired flight path to the assigned runway).
Conventional autopilot systems do not allow a change in ILS tuning with the autopilot engaged. Thus, in order to transition to a late runway change in a conventional autopilot system, the flight crew must go through a procedure to disengage the autopilot, manually fly the plane, re-tune to the new ILS approach, and then, if appropriate, re-engage the autopilot and select appropriate roll and pitch modes of the autopilot and, if desired, steer the airplane into a position for a manual landing, or into a position to recapture localizer and glideslope for the new runway assigmnent.
Approach is, however, one of the highest workload conditions a flight crew experiences. As such, it would be highly desirable if the autopilot could remain engaged during a transition to a late runway assigmnent and thereby alleviate flight crew workload.